Current supplied to cells of electrochemical plants, with particular reference to metal electrowinning or electrorefining plants, may be apportioned to the individual cell electrodes in a very diverse and inhomogeneous way, negatively affecting the production. This kind of phenomena can take place due to a number of different reasons. For instance, in the particular case of metal electrowinning or electrorefining plants, the negatively polarised electrodes (cathodes) are frequently withdrawn from their seats in order to allow harvesting the product deposited thereon, to be put back in place later on for a subsequent production cycle. This frequent handling, which is generally carried out on a very high number of cathodes, often brings about an imperfect repositioning on the bus-bars and far from perfect electrical contacts, also due to the possible formation of scales on the relevant seats. It is also possible that product deposition take place in an irregular fashion on the electrode, with formation of product mass gradients altering the profile of cathode surfaces. When this occurs, a condition of electrical disequilibrium is established due to the anode-to-cathode gap which in fact is not constant anymore along the whole surface: the electrical resistance, which is a function of the gap between each anode-cathode pair, becomes variable worsening the problem of unevenness in current distribution.
Current can thus be apportioned to each electrode in different amounts, both due to bad electrical contacts of the electrodes themselves with the current collecting bus-bars and to the alteration of the cathode surface profile. Moreover, even the simple anode wear may affect current distribution.
These inhomogeneities in current distribution can lead to anode-cathode short-circuiting phenomena. In the event of a short-circuiting, current tends to concentrate on the short-circuited cathode subtracting current to the remaining cathodes and seriously hampering production, which cannot be restored before the short-circuited cathode is disconnected from the cell.
Furthermore, an irregular current distribution, besides provoking a loss in quality and production capacity as mentioned above, would challenge the integrity and lifetime of anodes of modern conception manufactured out of titanium meshes.
In industrial plants, given the high number of cells and electrodes that are present, the task of spotting irregularities in current distribution is a very complex one. Such a detection involves in fact thousands of manual measurements, carried out by operators by means of infrared or magnetic detectors. In the specific case of metal electrowinning or electrorefining plants, operators execute such detections in a very warm environment and in the presence of acid mists, mainly containing sulphuric acid.
Moreover, conventional manual elements used by operators, such as gaussmeters or instruments with infrared sensors, allow locating only big current distribution disequilibria, since what they really detect are unbalances associated with magnetic field or temperature variations.
These manual or semi-manual systems have the disadvantage of not working in continuous, only allowing to execute occasional checks, besides being very expensive.
There are known wireless systems for cell monitoring that, although being permanent and operating in continuous, can only detect voltage and temperature variations for each cell and not for each single electrode. For the above explained reasons, this information is scarcely accurate and globally insufficient. Moreover, there are developmental projects aiming at the continuous detection of current supplied to individual cathodes by fixed current sensors relying on Hall effect: such sensors are active components requiring a big size external power supply, for instance a large set of batteries.
Systems based on magnetic sensors are also known, however they do not offer a sufficient accuracy of measurement.
For these reasons, there exist the need by the industry of a technically and economically viable system for permanently and continuously monitoring current distribution in all electrodes installed in an electrowinning or electrorefining plant.